The present invention relates generally to semiconductor fabrication, and more particularly to methods for establishing inter-layer dielectrics (ILD) for semiconductors having small gaps between metal lines 0.25xcexc technology.
Semiconductor chips or wafers are used in many applications, including as integrated circuits and as flash memory for hand held computing devices, wireless telephones, and digital cameras. Regardless of the application, it is desirable that a semiconductor chip hold as many circuits or memory cells as possible per unit area. In this way, the size, weight, and energy consumption of devices that use semiconductor chips advantageously is minimized, while nevertheless improving the memory capacity and computing power of the devices.
In chips that hold integrated circuits, the individual circuit components are interconnected by conductive elements referred to as xe2x80x9cinterconnect linesxe2x80x9d. These interconnect lines are typically arranged in a multi-layered pattern that is deposited on a semiconductive substrate such as silicon. To insulate the interconnect lines from each other, insulative material is deposited between adjacent interconnect line layers.
With the above in mind, so-called 0.25 micron technology has been developed, in which the distance between adjacent layers of interconnect lines in an integrated circuit on a semiconductor chip is equal to or less than about three-eighths of a micron. With such a small spacing between interconnect lines, which have heights of about 1.1 microns, the size of the circuits on the chip can be reduced to result in the above-noted advantages.
Typically, each electrically conductive interconnect line is made of a xe2x80x9cstackxe2x80x9d of metal layers that typically includes a layer made of aluminum or aluminum alloy, and one or more other metal layers. The aluminum is deposited as a film over the substrate and is then lithographically patterned and chemically etched to form a desired pattern for the circuit""s connector lines. Then, a process referred to as high density plasma (HDP) inter-layer dielectric (ILD) formation is used to fill the gaps between adjacent metal stacks with an electrically non-conductive material.
HDP ILD formation is preferred for 0.25xcexc technology over the older plasma enhanced chemical vapor deposition (PECVD) process. When ILD is deposited over and between the stacks, voids can form in the ILD between the stacks. Such void formation would reduce the insulation between adjacent stacks and thus lead to undesirable short circuits within the chip. In the PECVD process, to avoid ILD void formation it is necessary to sequentially deposit ILD and then etch away excess ILD, with repeat iterations being necessary to ensure that voids do not form in the ILD between the stacks. It happens that as the distance between adjacent stacks is decreased to the 0.375xcexc range, the problem of void formation is exacerbated and, hence, the shortcomings of the PECVD process magnified. On the other hand, in the HDP process the ILD material is deposited over and between the interconnect lines while simultaneously being sputtered away, thereby avoiding the formation of voids in the insulative material between the closely-spaced metal stacks while reducing fabrication time and, thus, increasing manufacturing throughput.
In HDP ILD formation, silane is used as the dielectric material. Silane has been preferred over tetraethoxy silane (TEOS) in 0.25xcexc semiconductor technology because it has a relatively high deposition rate, thus allowing for faster fabrication of the chips (and, hence, higher manufacturing throughput). Moreover, the process using silane is relatively easy to control with excellent quality. Also, silane is relatively inexpensive, compared to TEOS.
As recognized herein and confirmed by tests conducted by the present assignee, however, silane produces free hydrogen gas during fabrication, and it is to this problem that the present invention is addressed. More particularly, as recognized by the present invention free hydrogen gas is adsorbed by the aluminum, resulting in undesirable embrittlement of the aluminum. This is undesirable because, as the present invention understands, such embrittlement can promote the subsequent formation of voids in the aluminum that can be caused by mechanical stresses. These stresses arise largely because the thermal expansion coefficient of the mechanically constrained aluminum layer is different from the thermal expansion coefficient of the encapsulating oxide and the silicon substrate. When a void forms in a thin aluminum line, the current path through the line unfortunately is diverted, thereby adversely affecting the reliability of the chip.
Fortunately, the present invention recognizes that contrary to previous methods, TEOS can be used as the inter-layer dielectric in 0.25xcexc semiconductors. More particularly, the present invention recognizes that because the use of TEOS results in the production of relatively little or no free hydrogen, hydrogen embrittlement of aluminum in 0.25xcexc semiconductors consequently can be significantly reduced or indeed eliminated by using TEOS instead of silane, thereby improving 0.25xcexc chip reliability.
A method is disclosed for making a semiconductor chip having electrically conductive interconnect lines. The method includes providing at least one substrate, and establishing at least one predetermined pattern of electrically conductive interconnect lines on the substrate. In accordance with the present invention, TEOS is then deposited between and on top of the lines by directing TEOS onto the lines while simultaneously removing excess TEOS. Preferably, the TEOS is removed by directing a sputtering agent against the TEOS at about a forty five degree (45xc2x0) angle.
In a preferred embodiment, the substrate includes a semiconductor, and each conductive line defines a stack that includes a layer of titanium on the substrate and a layer of aluminum or aluminum alloy on the layer of titanium. Preferably, the establishing step includes depositing a layer of aluminum film and etching the film to establish the predetermined pattern. As disclosed in detail below, the step of etching the aluminum film is accomplished using a chemical etchant. On the other hand, the step of sputtering the TEOS is accomplished using argon gas. A chip is also disclosed that is made by the above process, and a computing device incorporating the chip is further disclosed.
In another aspect, a semiconductor chip includes at least one substrate, and at least one predetermined pattern of aluminum lines is supported by the substrate. Adjacent lines are separated by distances equal to or less than about three-eighths of a micron. Moreover, a TEOS dielectric material is between at least the first and second lines.
In still another aspect, a method for making a semiconductor chip includes establishing plural electrically conductive lines on at least one substrate, with at least some lines being spaced from each other by distances equal to or less than three-eighths of a micron. Additionally, the method includes depositing TEOS between at least two lines that are adjacent each other, such that little or no free hydrogen is produced during the depositing step.
Other features of the present invention are disclosed or apparent in the section entitled: xe2x80x9cDETAILED DESCRIPTION OF THE INVENTION.xe2x80x9d